1. Field of the Invention
The present invention relates to a distance measuring apparatus, and particularly to a distance measuring apparatus of, for example, a camera, using passive AF sensors.
2. Description of the Related Art
A distance measurement using a passive AF sensor is known as a process of imaging a distance measurement object by, for example, a pair of left and right line sensors and calculating the distance from the distance measurement object according to the amount of deviation between left and right sensor images obtained by the left and right line sensors (refer to Japanese Patent Application Publication Nos. 8-285580 and 11-23957, and Japanese Patent No. 3099603, etc.).
Conventionally, in the AF sensor, signals (luminance signals) outputted from cells (light receiving elements) of each line sensor are integrated for each cell so that sensor images with an appropriate amount of light is obtained whether the distance measurement object is bright or dark, and when the signal amount level of sensor data obtained by the integration reaches a certain level, the integration ends and an integration end signal is outputted from the AF sensor. A CPU carrying out distance calculation acquires the sensor data from the AF sensor when the integration end signal is outputted from the AF sensor, and calculates the distance from the distance measurement object according to the sensor data. On the other hand, if the distance measurement object is very dark, there are cases where the integration end signal is not outputted from the AF sensor even after integration processing in the AF sensor is continued for a certain amount of time, and in these cases, it is determined that distance measurement is impossible because the distance measurement object is dark.
However, even though the integrated signals in the AF sensor can not reach the signal amount level equivalent to the end of integration, distance measurement may be possible if some level of signal amount is obtained. In this case, it is not appropriate to determine that distance measurement is impossible because the integration end signal is not outputted.
The present invention has been devised in view of the above situations, and the object thereof is to provide a distance measuring apparatus that can perform distance measurement without determining that sensor data is invalid as long as sensor data with which distance measurement can be carried out is obtained in the AF sensor even if the integration end signal is not outputted from the AF sensor in distance measurement using a passive AF sensor or the like.
In order to attain the above-described object, the present invention is directed to a distance measuring apparatus, comprising: an AF sensor which forms images of light from a distance measurement object on a pair of line sensors comprising a plurality of light receiving elements and performs integration of signals obtained from the light receiving elements for each of the light receiving elements to generate sensor data, and ends the integration and outputs an integration end signal indicating the end of the integration when a predetermined integration end condition is satisfied; an AF sensor controlling device which instructs the AF sensor to start the integration; and a distance measurement object distance calculating device which calculates a distance from the distance measurement object according to the sensor data generated by the integration in the AF sensor, wherein: if the integration end signal is outputted from the AF sensor before maximum acceptable integration time accepted as time of the integration elapses after the AF sensor is made to start the integration, the AF sensor controlling device determines that the sensor data generated by the integration is valid, and if the integration end signal is not outputted from the AF sensor even after predetermined time elapses after the AF sensor is made to start the integration, the AF sensor controlling device evaluates a signal amount level of the sensor data generated by the integration and determines whether the sensor data generated by the integration is valid or invalid according to the evaluated signal amount level; and the distance measurement object distance calculating device calculates the distance from the distance measurement object according only to the sensor data determined to be valid by the AF sensor controlling device.
Preferably, the predetermined time is the maximum acceptable integration time.
Preferably, when the AF sensor controlling device determines that the sensor data generated by the integration is invalid, the distance measurement object distance calculating device does not perform calculation of the distance from the distance measurement object according to the sensor data determined to be invalid and determines that distance measurement is impossible.
Preferably, the AF sensor controlling device designates in the AF sensor a plurality of selection areas into which a distance measurement area of each of the line sensors is divided, one after another to have the integration carried out each time each selection area is designated; when the selection area indicating a range of light receiving elements of each of the line sensors is designated, the AF sensor determines whether the integration end condition is satisfied or not solely with the integration signals obtained from the designated selection area; and the distance measurement object distance calculating device calculates the distance from the distance measurement object according to the sensor data generated by the integration in each designated selection area at the time when the each selection area is designated, and determined to be valid by the AF sensor controlling device.
Preferably, the distance measurement object distance calculating device divides the distance measurement area of each of the line sensors of the AF sensor into a plurality of divided areas to calculate the distance from the distance measurement object with each of the plurality of divided areas, determines the distance from the distance measurement object for use in focusing control according to the distances of the distance measurement object calculated with the plurality of divided areas, and when calculating the distance from the distance measurement object with the plurality of divided areas, calculates the distance from the distance measurement object only with the divided area in which the sensor data determined to be valid by the AF sensor controlling device is obtained.
Preferably, the integration end condition includes a condition where a peak value of the sensor data generated with each of the light receiving elements reaches a fixed value.
According to the present invention, the signal amount level of sensor data generated by the AF sensor is evaluated to determine whether the sensor data is valid or invalid even if the integration end signal is not outputted from the AF sensor, thus making it possible to determine the distance from the distance measurement object with the sensor data considered valid as long as a signal amount level with which distance measurement can be carried out is achieved even if sensor data generated in the AF sensor does not satisfy integration end conditions. Therefore, the likelihood of problems such that it is determined that distance measurement is impossible more than necessary can be lessened.